21505015 has 16 divisors (see below), whose sum is σ = 30051648. Its totient is φ = 14466816.

The previous prime is 21505013. The next prime is 21505019. The reversal of 21505015 is 51050512.

It is not a de Polignac number, because 21505015 - 2¹ = 21505013 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21504983 and 21505001.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21505013) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3942 + ... + 7651.

It is an arithmetic number, because the mean of its divisors is an integer number (1878228).

Almost surely, 2^21505015 is an apocalyptic number.

21505015 is a deficient number, since it is larger than the sum of its proper divisors (8546633).

21505015 is a wasteful number, since it uses less digits than its factorization.

21505015 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11658.

The product of its (nonzero) digits is 250, while the sum is 19.

The square root of 21505015 is about 4637.3499975740. The cubic root of 21505015 is about 278.0865067292.

Adding to 21505015 its reverse (51050512), we get a palindrome (72555527).

It can be divided in two parts, 21 and 505015, that multiplied together give a triangular number (10605315 = T₄₆₀₅).

The spelling of 21505015 in words is "twenty-one million, five hundred five thousand, fifteen".